This invention relates to an apparatus and a method for individually separating outer sheets or outer sets of sheets of a stack.
Such an apparatus and such a method are known from Dutch patent specification 10 02743, In this known apparatus, the separation is carried out by placing a suction mouth against an outer sheet and thereupon creating a reduced pressure in the suction mouth. Thereupon the suction mouth is moved away from the stack, while the sheet, owing to the reduced pressure, is held against the suction nozzle and is thereby, at least locally, carried along. Thereafter, a separation element is brought between the sheet and the stack, which engages the sheet and separates it further from the stack and moves it away from the stack. Instead of sheets, sets of sheets can be separated, such as sets of sheets bound to form quires or booklets, or envelopes with sheets inserted in them.
To obtain a reliable operation in such a system, the reduced pressure needs to be set fairly accurately in accordance with the properties of the sheet or sets of sheets to be separated. This is objectionable in particular when the properties of the sheets within a stack or in different stacks vary. More particularly, the suction force must be strong enough to displace the sheet or the sets of sheets, but must not be so strong that suction is applied through the sheet, thereby causing a next sheet to be moved away from the stack as well, or that the outer sheet is damaged.
Further, the suction mouth, which, with a view to a proper sealing, must be made of pliable material, in each case touches the sheet to be separated. This limits the life of the suction mouth and sometimes causes prints on the outer sheet.